Photos of the Long Island Sound

About the Sound

A Glossary of LISS Related Terms


Algae – Rootless plants that grow in estuaries and “feed” on nutrients (such as nitrogen and phosphorus) in the water.

Algae blooms – Excessive algae growth that occurs when too many nutrients are present in the water.

Anadromous fish – Fish that spend most of their lives in saltwater, but migrate into freshwater tributaries to reproduce (spawn).

Anoxic – Water that is absent of dissolved oxygen, which can result in significant, adverse ecological effects in the bottom water habitats of the Sound.

Anadromous fish passage – A structure built to allow fish to swim around a barrier (such as a dam) in a stream during migration from saltwater to freshwater.

Atmospheric deposition – Process by which contaminants in the air return to the earth’s surface. Air pollution washed out of the sky by rain or snow is called “wet deposition.” When air pollution deposits without benefit of rain, it is called “dry deposition.”

Catadromous – Fish species that live primarily in freshwater, such as lakes, ponds and rivers, but migrate to sea to spawn.

Chlorophyll a – A pigment in plants that is used to turn light energy into food. Chlorophyll also gives plants their green color.

Clean Water Act – The law that establishes the basic structure for regulating discharges of pollutants into waters of the United States. The Clean Water Act prohibits unpermitted discharges of any pollutant from a point source into navigable waters and recognizes the critical problems posed by nonpoint source pollution. Section 320 of the Clean Water Act directs EPA to develop plans for attaining or maintaining water quality in estuaries. This includes protection of public water supplies and the protection and propagation of a balanced, indigenous population of shellfish, fish, and wildlife, and allows recreational activities in and on the water.

Comprehensive Conservation and Management Plan (CCMP) – Each of the National Estuary Programs (NEPs) is required to develop a Plan that identifies the specific commitments and recommendations to maintain and improve the waters of their estuary. LISS’s CCMP works to protect and restore LIS by improving water quality, protecting habitat and living resources, educating and involving the public, improving the long–term understanding of how to manage the Sound, monitor progress, and redirect management efforts.

Diadromous– Fish species that use both marine and freshwater habitats during their life cycle.

DichloroDiphenylTrichloroethane (DDT) – A persistent organic pollutant that was commonly used in pesticides before it was banned for agricultural use in most developed countries.

Dissolved oxygen – Microscopic bubbles of oxygen that are mixed in water. Dissolved oxygen is necessary for healthy lakes, rivers, and estuaries. Fish will drown in water if the dissolved oxygen levels get too low (hypoxia – see below).

Endocrine disrupting chemical – A synthetic chemical that when absorbed into the body either mimics or blocks hormones and disrupts the body’s normal functions. Chemicals that are known endocrine disruptors to humans and wildlife include dioxin, PCBs, DDT, and some other pesticides.

Environmental Indicator – Quantitative measurements that are used to track water quality, coastal habitats, and populations of key species in Long Island Sound and along its shores.

Estuary – A semi–enclosed body of water that has a free connection with the open sea and within which seawater (from the ocean) is diluted measurably with freshwater that is derived from land drainage (i.e., from the Connecticut River).

Eutrophication – A condition in aquatic ecosystems where high nutrient concentrations stimulate blooms of algae, thereby resulting in low dissolved oxygen levels in the water.

Freshwater – Water from rivers, lakes, reservoirs and underground streams.

Hydrology – The scientific study of the properties, distribution, and effects of water on the earth’s surface, in the soil and underlying rocks, and in the atmosphere.

Hypoxia – Low dissolved oxygen concentrations in water that result in significant, adverse ecological effects in the bottom water habitats of the Sound.

National Estuary Program – Program established by Congress in 1987 to improve the quality of estuaries of national importance. Each program develops a Comprehensive Conservation and Management Plan to meet the goals of Section 320 of the Clean Water Act.

Nitrogen – A nutrient that fuels the growth of algae, resulting in low oxygen waters (hypoxia) when the algae die and subsequently decompose.

Nonpoint source – A diffuse source of pollution that cannot be attributed to a clearly identifiable, specific physical location or a defined discharge channel.

Pathogens – Microorganisms such as viruses, bacteria and parasites that can cause illness in people exposed to them through swimming in, or consuming fish or shellfish from, contaminated waters.

Point source – Pollution that comes from a single location, such as a sewage discharge pipe.

Polychlorinated biphenyls (PCBs) – A group of synthetic, toxic industrial chemical compounds once used in making paint and electrical transformers. Although virtually banned in 1979 with the passage of the Toxic Substances Control Act, PCBs continue to appear in the flesh of fish and other animals.

Pycnocline – The natural stratification of the Sound’s waters that occurs during the summer when warmer, fresher water floats on the cooler, saltier water that is more dense. The density difference between these two layers prevents the mixing of the well–oxygenated surface waters with the bottom waters. – website

Riparian buffer – Vegetative areas next to rivers, streams, and lakes that naturally filter pollutants from runoff, stabilize banks, and provide habitat for wildlife.

Runoff – Water that flows across the surface of the land and drains into a water body.

Salinity – A measure of the salt concentration of water, usually measured in parts per thousand (ppt). Higher salinity means more dissolved salts.

Stewardship – Taking care of the natural resources that we use in our daily lives and administering those resources so they are available for the use and enjoyment of others, including future generations.

Submerged aquatic vegetation (SAV) – Rooted vegetation that grows under water in shallow zones where light penetrates.

Total Maximum Daily Load (TMDL) – A sum of the maximum amount of a pollutant that a water body can receive from all contributing point and nonpoint sources and still meet water quality standards.

Toxics – Organic and inorganic substances in water and sediments that can cause adverse human and ecosystem health effects.

Watershed – The area of land that drains into a particular body of water.

Wetland – The transitional zone between land and submerged systems that naturally store flood water, protect the land from erosion and storm, filter pollutants from runoff, and provide habitat for wildlife.

Sound Facts



Late each summer, much of the water in Long Island Sound is trapped beneath a ‘pycnocline,’ the layer that divides lighter surface waters from the denser deep waters. Because it doesn’t mix with surface waters, this bottom water may have insufficient oxygen for fish, lobsters and other animals to live.
Learn more about this fact
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